let's first take you to our current stable (6.6.3): The support for this version will not be dropped! This means that we are going to do our best to backport bugfixes that are done in ZeosLib 7 and maybe add new translations. Bugfixes will only be implemented on 6.6 when they are safe and non-intrusive! They are available from svn in /branches/6.6-patches. We are planning to release so called "patch packages" that will be named 6.6.n.-stable. Those patch packages will contain critical bug fixes, translations (as mentioned above) or new/modified package files for IDE changes.

The text you are quoting is a few years old. In the meantime stable versions 7.0 and 7.1 are released.So now we effectively stopped supporting the 6.6 version. You only need that series when still using very old compilers (e.g. Delphi 5 or 6).For these compilers we can safely assume latest 6.6 works fine.